First Water Choke

[bill-mcnamara]

Another question gents;
The vacumm line (#4 in Franks’s diagram) was chewed as mentioned in first post, where it looped way up near the starter bracket. The line then drops back down to a nipple in the intake manifold close to the carb boss.
I’m curious as to why the line took such a circuitous route? looks almost like an anti-syphon device, but for what? Shouldn’t be any fluids in there anyway.
Any ideas???

I cut out about 3" and the hose led comfortably (no kinking) to the nipple more directly without the upward detour, as an experiment.

[rvpapasso]

The only reason I can see for excessive length of the vacuum line may be to make the carb easier to remove. Things are a little tight around the carb and maybe having excess length allows the carb to be removed to get better access to the vacuum line where it connects to the pull off or the manifold connection. You are correct that there are no fluids present where an anti-siphon would be required. You should also not need excess line to act as a vacuum reserve.

As Frank mentioned there is a careful balance of springs to make the automatic choke work. When the engine is not running the spring in the vacuum pull off is trying to keep the choke closed against the thermostatic spring that is trying to open to the choke to a position based on engine temperature. As stated the vacuum pull off will release the choke when there is intake manifold vacuum. In order to have the vacuum pull off release the choke with the minimum amount of vacuum during low RPMs the spring in the pull off is not excessively strong, just enough to do the job of overcoming the thermostatic spring. Therefore even a slight amount of intake manifold vacuum pulsations will reduce the ability of the spring in the vacuum pull off to keep the choke closed firmly.

If the manual choke lever is used to close the choke there is no flutter since the manual choke lever locks the choke closed regardless of any spring trying to open the choke.

This system was employed for decades on cars with carburetors that had the “Carter Climatic Control”. When maintained properly and adjusted properly it works great. As I said I have had no problems for over 19 years with this type of choke on my 1960 40Hp Johnson. Easy starting with a turn of the key, hot or cold, and smooth warm up.

Once you understand how it works and can actually see it function it all becomes pretty clear and quite simple. Unfortunately the simplicity is lost in the details without having one in your hand.

[benchrascal]

That was a really good explanation of the way that choke is supposed to work Frank ,always wondered ,never knew.When you mentioned your friend’s new motor woes it brought two "choke " stories to mind ,both newer motors.I listed a boat with a commercial 65 Evinrude "at a Dealer" for sale and got a panicked phone call from the salesman "The motor will not start!" he had a customer that was going to walk .Dropped everything and ran out there and did exactly as you did ,raised lever ,pushed key and turned ,started instantly ,lord knows what they had tried prior to that .Second instance I went fishing with a friend and ended up on the tiller of his newer Merc product .Advanced the cold throttle ,primed it once and pulled ,bingo it started right away .He was amazed ,turned out he never thought it had a prime always thought it was a standard choke and pulled it about twenty times to get it to start .he was pretty sheepish when I explained how it really worked.

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